The present invention relates to a swing control apparatus of construction equipment and control method thereof, and more particularly, a swing control apparatus and method for construction equipment, in which the machine is capable of making a swing angle reach a target angle by controlling a braking torque of a swing motor during the loading operation of an excavator.
In general, excavators are well known in the an and for use in a loading operation work. The loading operation work may include a scooping excavation of scooping up the earth and sand using a bucket, a swing operation of swinging or revolving an upper swing body, a dumping operation of loading the earth and sand to the dump truck and a return swing operation of returning the upper swing body to a position associated with the scooping excavation.
FIG. 1 is a hydraulic circuit diagram of a swing control apparatus of construction equipment according to the conventional technology.
In FIG. 1, first and second variable displacement hydraulic pumps (hereinafter, the first and second hydraulic pumps)(1, 2) and a pilot pump (3) are connected to an engine (4).
Boom cylinder (5), arm cylinder (6) and bucket cylinder (7) which drive the boom, arm, and bucket by hydraulic fluid supplied from the first and second hydraulic pumps (1, 2) are connected to the first and second hydraulic pumps (1, 2).
A control valve of the work device (MCV) (8) for controlling the supply of the hydraulic fluid from the first and second hydraulic pumps (1, 2) is installed in flow paths of the first and second hydraulic pumps (1, 2).
The second hydraulic pump (2) is connected to a swing motor (9) for swinging the or revelving the upper swing body (13) which is driven by hydraulic fluid supplied from the second hydraulic pump (2).
A swing control valve (MCV) (10) is installed in a flow path between the second hydraulic pump (2) and the swing motor (9). A swing operation lever (11) (RCV) for applying a pilot pressure in order to shift the swing control valve (10) is installed in a path between the pilot pump (3) and the swing control valve (10).
Inside the swing motor (9) are installed relief valves (12a, 12b) for controlling a swing braking torque of the swing motor (9).
The relief pressures of the relief valves (12a, 12b) are preset and given by a spring force of the valve spring. Thus, the maximum torque of the swing motor (9) is limited by the preset relief pressure of the relief valve (12a, 12b) That is, the torque is limited up to the maximum based on the preset relief pressure of the relief valve (12a, 12b) when the swing motor (9) is accelerated or decelerated to the maximum level.
Moreover, when the work devices such as boom, arm and bucket are operated during a swing operation of the upper swing body, the inertia moment of rotation of the upper swing body varies, making it more difficult to control a swing angle so that it reaches a target angle.
It is desirable to provide a swing control apparatus for construction equipment and a method thereof for making a swing angle reach a target angle even when the inertia moment of an upper swing body is varied as the work devices are operated on a return swing in the process of the loading operation of the excavator.
In accordance with an aspect of the present invention, there, is provided a swing control apparatus for construction equipment comprising:    first and second hydraulic pumps and the pilot pump;    a work devices including a boom, an arm and a bucket which are operated by a boom cylinder, an arm cylinder and a bucket cylinder driven by hydraulic fluid of the first and second hydraulic pumps;    a work device control valve for controlling hydraulic fluid supplied from the first and second hydraulic pumps;    a swing motor for swinging an upper swing body which is driven by hydraulic fluid supplied from one of the first and second hydraulic pumps;    a swing control valve for controlling hydraulic fluid supplied to the swing motor from the first or second hydraulic pump;    a swing operation lever;    a direction control valve for applying to the swing control valve a pilot pressure supplied by operating the swing operation lever, or a pilot pressure supplied by selecting a semiautomatic swing mode;    at least one electronic proportional variable relief valve installed in the swing motor, which variably controls a preset relief pressure so as to vary a braking torque of the swing motor; and a controller for applying an electric control signal to the electronic proportional variable relief valve to be relieved so that the relief pressure of the electronic proportional variable relief valve is preset to increase or decrease in order to make a target swing angle become the sum of a swing braking angle predicted from the inertia moment of the upper swing body plus a swing angle detected of the upper swing body, when the semiautomatic mode is selected and the work device is operated during a return swing of the upper swing body.
According to an embodiment of the present invention, there is provided a swing control method for construction equipment, including first and second hydraulic pumps and a pilot pump;    a work device including a boom, an arm and a bucket, which are operated by a boom cylinder, an arm cylinder and a bucket cylinder, respectively, driven by the hydraulic fluid of the first and second hydraulic pumps;    a work device control valve which is configured to control hydraulic fluid supplied from the first and second hydraulic pumps to the boom cylinder, arm cylinder and bucket cylinder, respectively;    a swing motor for swinging an upper swing body which is driven by the hydraulic fluid supplied from one of the first and second hydraulic pumps;    a swing control valve for controlling the hydraulic fluid supplied to the swing motor from the first or second hydraulic pump;    a swing operation lever;    a direction control valve for applying to the swing control valve a pilot pressure supplied by operating the swing operation lever, or a pilot pressure supplied by selecting a semiautomatic swing mode;    an electronic proportional pressure control valve for applying the hydraulic fluid from the pilot pump to the swing control valve through the direction control valve, if the semiautomatic swing mode is selected;    an electronic proportional variable relief valve which variably controls a preset relief pressure so as to vary a braking torque of the swing motor;    a swing angle sensor for detecting a swing angle of the upper swing body;    displacement sensors for detecting the displacements of the boom, arm, and bucket, respectively, during a return swing of the upper swing body; and    a controller for applying an electric control signal and adjusting the preset relief pressure of the electronic proportional variable relief valve by the electric control signal during a return swing of the upper swing body, the method comprising:    a step of selecting the semiautomatic swing mode;    a step of shifting the direction control valve so that the pilot pressure regulated by the electronic proportional pressure control valve is applied to the swing control valve, if the semiautomatic swing mode is selected;    a step of determining whether or not the sum of a predicted swing braking angle plus the swing angle detected of the upper swing body is equal to a target swing angle;    a step of shifting to a neutral state of the swing control valve by blocking the pilot pressure applied to the swing control valve, if the sum of the predicted swing braking angle plus the swing angle detected of the upper swing body is equal to the target swing angle;    a step of determining whether the swing angle of the upper swing body reaches the target swing angle; and    a step of shifting the direction control valve so that a pilot pressure by operating of the swing operation lever is applied to the swing control valve, if the swing angle of the upper swing body reaches the target swing angle.
The swing control apparatus further comprises an electronic proportional pressure control valve which is configured to apply a pilot pressure to the swing control valve, wherein the pilot pressure from the pilot pump is adjusted by convening an electrical current value that corresponds a maximum operation amount of the swing operation lever, if the semiautomatic swing mode is selected.
The swing operation lever includes a selection switch for selecting the semiautomatic swing mode which turns off when the swing operation lever is operated during the return swing of the upper swing body. The controller includes a PD controller for applying a calculated electrical current value to the electronic proportional variable relief valve to be relieved, in which the PD controller is performed with the target swing angle of PD control inputted by the sum of the swing braking angle predicted from the inertia moment of the upper swing body plus the swing angle detected of the upper swing body so that the target swing angle can be reached by compensating the inertia moment of the upper swing body, which varies when the work device is operated during the return swing of the upper swing body.
The swing control apparatus further comprises displacement sensors for detecting the displacements of the boom, arm, and bucket during the return swing of the upper swing body, and a swing angle sensor for detecting the swing angle of the upper swing body and outputting the detected swing signal to the controller The method further comprises a step of applying the electrical signal to the electronic proportional variable relief valve to be relieved so that the relief pressure of the electronic proportional variable relief valve is preset to increase or decrease in order to control the target swing angle to be the sum of the swing braking angle predicted from the inertia moment of the upper swing body plus the swing angle detected of the upper swing body, when the work device is operated during the return swing of the upper swing body. The swing braking angle of the upper swing body is predicted from the inertia moment of the upper swing body which is calculated by the angles of the boom, arm and bucket detected by displacement sensors of the boom, arm, and bucket during the return swing of the upper swing body.
The method further comprises a step of proceeding to step of shifting the direction control valve so that the pilot pressure regulated by the electronic proportional pressure control valve is applied to the swing control valve, if the sum of the detected swing angle of the upper swing body plus the predicted swing braking angle is not equal to the target swing angle.
The method further comprises a step of proceeding to step of applying the electrical signal so that the relief pressure of the electronic proportional variable relief valve is preset to increase or decrease, if the swing angle of the upper swing body does not reach the target swing angle.
According to the embodiment of the present invention having the above-described configuration, a target swing angle can be reached by controlling a braking torque by varying a preset relief pressure of an electronic proportional variable relief valve, even when the inertia moment of an upper swing body is varied as the work device is operated in the process of the return swing of the upper swing body during the loading operation.
Explanation of reference numerals for main parts in the drawing    1; first hydraulic pump    2; second hydraulic pump    3; pilot pump    4; engine    5; boom cylinder    6; arm cylinder    7; bucket cylinder    8; work device control valve    9; swing motor    10; swing control valve    11; swing operation lever    13; upper swing body    14, 15; direction control valve    16, 17; electronic proportional variable relief valve    18; controller    19, 20, 21; displacement sensor    22; swing angle sensor    23, 24; electronic proportional pressure control valve